Automatic medicament delivery devices, such like auto-injectors provide a rather easy and convenient approach to inject a predefined dose of a liquid medicament into biological tissue. Such drug delivery devices may provide an injection needle extension and retraction mechanism in order to puncture biological tissue to which the liquid medicament is to be delivered. After the injection needle has been extended into an injection position drug delivery through the injection needle may automatically start. After termination of a delivery process the needle is typically retracted back into the housing. Since such drug delivery devices are intended for home- or self-medication their general handling should be easily understandable and unambiguous.
Additionally, such devices should provide a high degree of patient safety in order to avoid stitch damages or similar injuries. Moreover, depending on the therapy, depending on the medication schedule as well as depending on the size of the dose of the liquid medicament to be injected, in some cases rather large injection volumes, e.g. larger than 1.25 ml and high viscosity of the liquid medicament may cause some difficulties and problems with existing drug delivery device designs. For instance, total time for the delivery of the medicament may be out of a predefined range. Moreover, the viscosity and the total volume of the liquid medicament could lead to patient discomfort.
Since such drug delivery devices are of portable or mobile type they are typically equipped with some kind of energy storage to displace the injection needle and to conduct a dispensing procedure. Document US 2012/0071829 A1 describes an apparatus featuring a medicament injector moveably disposed within a housing and an energy storage member configured to produce a force to move the medicament injector to an injection position in which a portion of a needle is disposed outside of a distal end portion of the housing. The energy storage member is a compressed gas cylinder that is operable to produce a force that acts upon the medicament container to move the same between a first position and a second position. In response to a force produced by the pressurized gas, a moveable member and the medicament injector are moved towards a distal end portion of the housing, thereby exposing the needle from the housing. Then, the moveable member continues to move within the medicament container to expel a medicament from the medicament container through the needle.
For activation of medicament delivery the compressed gas cylinder is to be displaced inside the housing from a first position into a second position, e.g. by way of a suitable spring element. There, not only a well-defined displacement of the compressed gas cylinder but also a gas tight coupling of the gas cylinder has to be provided when it reaches its second position. The housing in which the pressurized gas cylinder is displaced therefore needs to be rather robust and requires a rather precise geometry.
Aspects of the invention may include an improved injection device for dispensing of a liquid medicament featuring an automatic sequence for the various steps of injection and drug delivery. The device should provide a particular high dispensing force, which is even suitable for dispensing and injecting of liquid medicaments featuring a particular high viscosity. Moreover, the injection device should be capable to dispense rather large volumes of liquid medicaments. The device should be user friendly and should provide a tactile and/or an audible feedback to indicate that the injection procedure has terminated. Additionally, the injection device should provide automatic injection needle extension and retraction prior to and after drug delivery. Additionally, the injection device should be rather lightweight. It should be easy to assemble and should be producible in a cost-efficient way, in particular by way of an industrial mass production process